Unfortunately I don’t have the data. (It is quite possible that being lazy, I never even tried looking for it)
And yes, I agree — there could have been different ways of implementing it, but each approach would have come with its own set of positives and negatives. For example, the approach you mentioned would have increased the number of action-buttons. As I said, I’m sure they are just experimenting and I’m inclined to give them points for making some bold moves.
(Btw, it’s not like I don’t have my own set of problems with Medium’s execution of things. One of them, which is aligned with this dialogue, is the usefulness of the paid membership. As you can see, I’m not a member. I had even been invited to be a part of the paid writers program, but I don’t think it is for me. I’ve always believed in knowledge should be free. But yeah, they are onto something. Let’s hope it is something good.)